Just a little experience I had with a student this week...
Johnny's* mother came in early before his lesson alone, frantically gesticulating and pacing, exclaiming that Johnny wanted to quit violin, that he hated it and every practice session was a session of tears and temper tantrums. She herself is a music teacher, so she understood that there's only so much a music teacher can say to parents, especially considering that although I have over 30 students I don't have any children of my own. I asked her, "What do you usually say to parents of your students who are going through the same thing?" She gave the usual reply, that all of us have gone through this, there are phases where children, especially preteens, don't want to do what their parents want them to, etc.; things I would say as well. I did my best to encourage her, but that was all I could tell her, too. I assured her that her son was doing very well, and was just at the point where he needed the encouragement to take it to the next level. I'd hate to see him quit, because he's a very good player and I enjoy teaching him.
After a few minutes Johnny came from class into the studio for his lesson. We did not mention what his mother and I had talked about; I thought I'd save it for the end. Johnny proceeded to play a few scales, review pieces, and a Vivaldi concerto. Everything he played had a feeling of tension and anger in it. It was truly amazing to me how much this little boy could express with his violin. I kept reminding him to slow down his shifts, relax his left hand for vibrato, and loosen his right elbow to smooth the sound. Toward the end of the lesson, I gave Johnny a little talk. I pretty much just told him, "Johnny, no matter what you feel, you have to be obedient to your mother, and practice just the way she asks you to. No temper tantrums are allowed; crying does NOT count as part of your practice time!" Then I told him: "I can tell simply by the way you are playing that you are angry. You have to understand how much your violin expresses the way you feel. It's great to express your feelings through your music, but you must control your anger."
As Johnny was putting his violin in its case at the end of the lesson, he listened intently to me as I told him and his mother, "You always hear about controversies involving musicians' unions and various theater companies and films wanting to save money by using 'canned' music, synthesizers, multi-track recordings and so on, as opposed to hiring live musicians. Sometimes people have even theorized that with so much technology that can produce computer-generated music, real, live musicians will become a thing of the past. But we can see that this is why there are musicians in the world. It's truly amazing how much you can express with your instrument. I get this all the time--parents tell me something about how practice is going at home, and immediately I can see what they mean from the first piece a student plays in the lesson." Believe it or not, this applies to Twinkle as well as Vivaldi concerti.
*not his real name; names changed to comply with HIPAA policy